1. Technical Field
This invention relates to a surgical trocar and more particularly to a safety trocar in which the sharp cutting tip retracts into the cannula so as to minimize the likelihood of inadvertent injury to viscera and other internal tissue.
2. Background of Related Art
Trocars are sharp pointed surgical instruments used to puncture a body cavity. Trocars are generally adapted to be used together with a tubular trocar sleeve or cannula. Once the body cavity has been punctured by the trocar, the sharp trocar is removed from the cannula, thereby leaving the cannula extending into the body cavity. Endoscopic surgical procedures are then performed through the cannula with accessory instrumentation such as laparoscopes, dissectors, graspers, etc.
Commercially available safety trocars include a spring-loaded safety shield which is adapted to cover the trocars tip once the body cavity has been entered so as to provide an increased level of protection to internal structures from puncture of laceration. For example, U.S. Pat. No. 4,601,710 to Moll describes a trocar assembly which consists of two subassemblies: a trocar subassembly which includes a sharp-tipped trocar and a spring-loaded tubular safety shield positioned therearound, and a cannula subassembly.
When ready for use, the trocar and safety shield of the trocar subassembly are inserted through the cannula. The safety shield is initially in its distal-most position covering the trocar tip. Exertion of pressure against the skin with the trocar causes the shield to be pushed rearwardly against the spring to expose the piercing tip of the trocar. The tip penetrates the skin and underlying tissue with continued pressure. Once the tip has penetrated through the wall and has entered the cavity, the force against the front end of the shield ceases and the shield is automatically moved back to its distally extended position. Viscera and other internal tissue are thus protected from contact with the sharp piercing tip and potential damage therefrom.
An article entitled “Needle for the Puncture and Lavage of the Abdominal Cavity” authored by F. S. Subairov discloses a safety device for puncturing the abdominal cavity which consists of a hollow tube, a stylet and a spring. The spring is soldered to the stylet and threaded into the rear of the hollow tube. The distal end of the stylet is exposed from the hollow tube by pressing the stylet toward the tube, thereby compressing the spring. Once the stylet and tube enter a body cavity, the tube is advanced under spring force to cover the distal end of the stylet. A similar device is disclosed in EP 350,291 (see FIGS. 1–4).
U.S. Pat. No. 4,535,773 to Yoon suggests several alternative safety trocar designs. In one embodiment (see FIGS. 22–28), a spring-loaded blunt probe is provided within the trocar shaft, as with conventional Verres needles. The blunt probe is adapted to reciprocally slide through an aperture in the trocar tip such that when the trocar tip enters a body cavity, the blunt probe springs distally forward through the aperture to prevent contact between the trocar tip and body organs. In a second embodiment (see FIGS. 33–36), pressure sensors or transducers are fitted into the trocar blade surfaces and the distal end of the cannula. Sets of electrical leads run through the trocar shaft and communicate with an alarm network in the proximal portion of the device. A further modification is suggested in which the trocar shaft is initially manually extended and maintained in its extended position by a detent which protrudes through a hole in the surrounding tubular structure. The hole aligns with a solenoid socket. When the instrument is fully assembled and the trocar tip is forced through a body wall, the electrical leads running through the trocar shaft send electrical signals to the solenoid which, at the appropriate instant, forces the detent from the hole, allowing the trocar tip to withdraw into the cannula. Additional mechanisms for effecting withdrawal of cutting implements are also known. See, e.g., U.S. Pat. No. 4,375,815 to Bums; U.S. Pat. No. 3,657,812 to Lee; and U.S. Pat. No. 3,030,959 to Grunert.